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The Design of Landfill Gas Extraction Pipework
The aim of the gas collection system is to extract the maximum possible volume of gas but to leave the condensate behind; landfill gas is warm and saturated with water. The proprietary make of well head used by many of the United Kingdom's landfill operators monitors and regulates the gas flow from each well, and also contains a barometric leg for draining condensate away. The gas flow regulation device used is best if it is specified to be sleeve valve type, which provides much finer adjustment than a butterfly valve. This is especially the case at low flows, and most importantly this more expensive valve choice does not restrict the condensate as can a butterfly valve.
The well heads are installed in line on the lateral pipe system. Choosing the correct diameter of pipe for the various sections of the system is of prime importance, since the velocity of the gas flow against the gradient of the pipe run is a critical factor in successful de-watering.
Pipelines are carefully laid to falls from well to well in order that the maximum amount of condensate is drained away via the well heads or other de-watering devices. It is a false economy to skimp on the number of individual pipelines used to transport the gas to the pumping station. It is good practice to have the collection system divided in to sections. This gives flexibility which is necessary e.g. if repairs have to be carried out due to damage by machinery or settlement. On an operational site it is sometimes necessary to remove and re-site sections of the collection system as filling of the site progresses.
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